The present invention relates to a method of manufacturing a thin-film magnetic device and, more specifically, to a method of manufacturing a thin-film magnetic device having a magnetic film provided with uniaxial magnetic anisotropy.
In a conventional method of manufacturing a thin-film magnetic device having an inductor structure, generally, a magnetic film is formed on a wafer and then heat-treated together with the wafer in a magnetic field in order to provide the magnetic film with uniaxial magnetic anisotropy. If, as illustrated in FIG. 1, a thin-film magnetic device is constituted by forming a magnetic film (FeCoBC) 3 having a thickness of several micrometers on a Si wafer 1 having a diameter of 100 mm or more with an insulation film 2 of SiO.sub.2 or SiN therebetween, there is a ratio of quadruple or more digits between the thickness of the magnetic film 3 and the size of the Si wafer 1; therefore, a demagnetizing field is suppressed on the magnetic film 3 and an external magnetic field is applied to the film 3 effectively.
Since, however, the stress of the magnetic film 3 is great, a crack 5 is easy to occur in the heat-treated magnetic film 3' due to a difference in stress between the magnetic film 3 and its underlying layer (wafer or insulation film) 4. The crack 5 degrades yield when the magnetic film 3' is divided into chips by the subsequent patterning.
If the underlying layer 4 is outgassed at the time of heat treatment, the gas is confined by the magnetic film 3' until the film 3' is divided into chips. For this reason, the magnetic film 3' comes off the underlying layer 4 or a blister occurs.
In order to resolve the above problems, as shown in FIGS. 3A, 3B and 3C, the magnetic film 3, which is formed on the Si wafer 1 with the insulation film 2 interposed therebetween, can be divided into chips and then subjected to heat treatment in the magnetic field. Since, in this method, the above-described difference in stress can be lessened by patterning the magnetic film 3 prior to the heat treatment, a crack can be prevented from occurring. Since, furthermore, gas is emitted from an exposed portion of the underlying layer 4, a blister can be prevented from occurring.
In the above method, however, the magnetic film 3 is cut short in a direction parallel to that of the magnetic field before the heat treatment and thus the magnetic characteristics of the magnetic film 3' deteriorates after the heat treatment.
It is generally known that the magnetic film 3, which is provided with uniaxial magnetic anisotropy, is excellent in magnetic characteristics if the ratio between the short side (which is perpendicular to the direction of the magnetic field) of the patterned film 3 and the long side (which is parallel to the direction of the magnetic field) thereof is larger.
However, when the magnetic film 3 is divided into chips each about several millimeters square, the ratio between the thickness of the magnetic film 3 and the size of the Si wafer 1 is about triple digits and thus a demagnetizing field is strengthened on the film 3. As a result, an external field is weakened, and uniaxial magnetic anisotropy cannot sufficiently be applied to the film 3 by the heat treatment in the magnetic field.